It has been well established that gravitational collapse, accretion disks, and bipolar outflows are basic building blocks in the formation process of low-mass stars.

However, it is still much debated whether high-mass stars form in a similar manner to low-mass stars. In order to investigate the infall motions (gravitational collapse) of high-mass star-forming regions, we performed single-pointing observations of 83 high-mass protostellar object candidates in the HCO+(1-0), HCO+(3-2), HCN(3-2), H2CO(2-1) and H13CO+(1-0) lines.

We detected infall signatures in the HCO+(1-0) transition for a statistically significant number of the sources, and found 29 infall candidates. In this talk, we will report the preliminary results and discuss the implications for high-mass star formation.